1. Field of Invention
The present invention relates to capacitors of the type consisting of wound or stacked alternating conducting layers and dielectric layers enclosed in a sealed case, and to a liquid dielectric composition suitable for impregnating such capacitors.
2. Description of Prior Art
A common type of electrical capacitor comprises a combination of spaced metal foil conductors having interposed therebetween a dielectric sheet which may be paper, polymeric film or a combination of paper and polymeric film. The dielectric sheet material and the interstices within the dielectric sheet and between the dielectric sheet and the conductors are impregnated with a liquid dielectric composition. Such impregnation is essential in order to realize the greatest dielectric strength of the dielectric material.
The preferred dielectric composition for impregnating capacitors has heretofore been polychlorinated biphenyl which has a relatively high dielectric constant and good low temperature properties. Certain of the polychlorinated biphenyls however, have now been discovered to be resistant to natural degradation and, when released into the environment, these materials may enter the life cycle and be potentially harmful to ecology. Even though capacitors are sealed units and escape of the impregnant into the environment can be prevented to a large degree, it has nevertheless become desirable to provide an alternate composition for impregnating capacitors which does not contain potentially harmful polychlorinated biphenyls.
It is accordingly an object of the present invention to provide a dielectric fluid composition for impregnating electrical capacitors which is free of polychlorinated biphenyls. It is a further object of this invention to provide capacitors containing said alternate dielectric fluid composition. Other objects of this invention will be apparent from the ensuing description and claims.